This invention relates to a transverse thermal sealer for sealing a packaging material used in a packaging machine for concurrently filling a bag with articles such as foods and making a packaged product.
A bag-making packaging machine for concurrently forming a bag, filling it with articles such as foods and making it into a packaged product, such as a so-called pillow-type packaging machine, is adapted to seal the mutually superposed longitudinal side edges of a belt-like elongated packaging material (hereinafter referred to as a film) while this film is being transformed into the shape of a bag by means of a former, and to thereafter transversely seal the bottom of the film, while the tubularly formed film is being pulled, by means of a pair of transverse thermal sealing means disposed below the outlet of the filling cylinder used for filling the tubular film with articles to be packaged. Since such a packaging machine is capable of simultaneously and continuously forming bags and filling them with articles to be packaged, it is considered an apparatus with high workability.
Japanese Patent Publication Tokkai 235006/87 disclosed an apparatus of the so-called rotary driving type adapted to cause the heating surfaces of its transverse sealing means to contact the film while the transverse sealing means are moved linearly in the direction in which the film is being pulled, such that a sufficiently long time can be spent for the transverse sealing process even if the period of cyclic packaging operation is shortened. For the purpose of causing the transverse sealing means to move in a linear trajectory, however, this apparatus makes use of D-shaped grooves to guide these means, while causing them to undergo a cyclic motion. In other words, their linear trajectory and the compressive force between them are uniquely determined, and the film may be subjected to an unreasonable force from them, depending on the thickness, material property and/or width of the film. As a result, the film may be damaged, or the apparatus may fail to reliably perform a transverse sealing process.
Packaging machines of the so-called intermittent driving type are also known. They are structurally simpler, although disadvantageous from the point of view of reducing the period of cyclic motion, and are characterized as pulling the film intermittently and carrying out the transverse sealing while the film is stopped. The method of using a hydraulic (oil-pressure) cylinder has been known in this connection for compressing the transverse sealing means against each other and adjusting the compressive force between them by controlling this pressure cylinder. Such a cylinder, however, tends to make the apparatus bigger as a whole, and there arises the problem of keeping the oil for the cylinder away from the articles to be packaged.
The present invention has been accomplished in view of these problems, and its first object is to provide a transverse sealer for a packaging machine of the rotary driving type (rotating type) capable of adjusting the compressive force between its transverse sealing means to a set level according to the thickness, material property and width of the film.
A second object of the invention is to eliminate the hydraulic cylinder from a packaging machine of the intermittent driving type such that the packaging machine can be made compact and the contamination by oil of articles to be packaged can be prevented.